1. Field of the Invention
The invention is directed to a power semiconductor module, more particularly a power semiconductor module with a deflection resistant plate.
2. Description of the Related Art
Power semiconductor modules that are the point of departure for the present invention are known for instance from German Patent Disclosure DE 103 16 355. Such power semiconductor modules have a base plate for thermal coupling to a heat sink. For that purpose, it is of particular importance to assure that the base plate, after the power semiconductor module has been secured, be as completely in thermal contact with the heat sink as possible, for the sake of an efficient heat transfer. In modern power semiconductor modules particular emphasis is placed on having a compact structure. Therefore the proportion of the surface of the substrate occupied by the power semiconductor components is especially high. Accordingly, these power semiconductor modules have connecting devices for connection to the heat sink only in their corner regions. Power semiconductor modules with high power levels, in particular advantageously have a structural shape in which the length is substantially greater than the width. It is preferable for the substrate to have a further metallization on its side which faces the base plate. By means of this metallization, the substrates are bonded materially to the base plate. In the prior art, this connection is established by means of soldering.
In power semiconductor modules with a comparatively great length, a soldered connection of the substrates and base plate can cause concave sagging in the base plate. Concave sagging is understood here to mean sagging in which the sagging of the middle region of the base plate is in the direction of the power semiconductor module, while convex sagging means sagging in the direction of the heat sink. A convex sagging of the base plate is advantageous for an efficient heat transfer between the power semiconductor module and the heat sink, since then the base plate, after being secured to the heat sink, rests flatly on the heat sink. In the event of concave sagging, a plane contact would not be established. Even during production, the base plates in the prior art are thus manufactured with convex sagging. Despite this so-called prestressing of the base plate, soldering of the substrates can lead to concave sagging of the base plate, unless the base plate is sufficiently rigid. Adequate rigidity is attained in the prior art by designing the base plate as correspondingly thick.
On the other hand, economical, compact production of a power semiconductor module requires a base plate with the least possible thickness. In the prior art, power semiconductor modules, especially with a substantially greater length than width, thus either have the disadvantage of a thick base plate or the disadvantage of concave sagging of a thinner base plate.